Recovery of liquid hydrocarbons from moisture-containing well fluids



June 10, 1941. R. F. FARRls 2,245,028

RECOVERY OF LIQUID HYDROCARBONS FROM MOISTURE-CONTAINING WELL FLUIDS Filed June 2, 1939 LIST/LATE S T0 E AGE DLS TIL Z/l T l. .SEPAP/l T018 Jill), l@

Patented June 10, 194i nEcovEaY'oF LIQUID maocsnlsoNs mom Mois'rimr:-ooN'rlunma; wm

FLUIDE Riley Floyd` Farris. Tulsa, Okla.,` assignor to t Stanolindl Oil and.E Gas Company, Tulsa,

' O kla., incorporation of Delaware Application June 2.1939, ssamms 276.950

f Fromm. 'This invention relates to the recovery of'liquid hydrocarbons from well fluids and more particu-l larly to improved methods and apparatus for economically recovering such hydrocarbons from the nuids produced by distillate wells which contain small quantities of moisture.

In recent years, however, certain I ields have been discovered from which the only yproducts (cica-122) l are natural gas and a relatively small amount 1 of a volatile hydrocarbon mixture which is called distillate. Some `wells have also been found which produce at a high gas-oil ratioI relatively small amounts of heavy hydrocarbons such as those usually associatedwith the term crude oil" together with the more volatile distillate.

My invention is concerned primarily with the recovery of distillate from distillate wells but also can be advantageously applied to wells or the latter type. These wells have many characteristics in common, including high pressure and high gas-oil ratio, and for purposes of simplicity Aus deilnite for each press' l' iluid composition and which increases with increase in pressure.` l

This temperature is hereinafter referred to as ,the "maximum temperatureoi hydrate formation, and tor a typical distillate-containing well fluid composition may be for example, about tno-o Ft at 500 pounds per square inch, (i5-70 F. atv 1000 pounds per square inch, and 75-80" F. at

2000 pounds per square inch. Since the yield of liquid distillate obtained increases markedly as .the temperature is lowered and the separator pressure employed is usually well in excess of' 500 pounds per square inch, the probleme! preventing hydrateiormation is a very real one in distillate recovery systems, particularly those or the retrograde condensation type. It has been proposea to eliminate hydrate formation by injecting an antirreeze liquid such as a concentrated calcium chloride brine solution directly into the well nuid prior to cooling and expansion and then separating the distillate and antifreeze under both will be referred to herein as distillate wells and the products therefrom as distillates. y

IZlhe reservoirs from which distillates are pro-- duced are invariably at high pressures and temperatures. for example 1500 to 4000 or more pounds per square inch and 125 F. to 250 F. .or

higher, and it is believed that in many cases the hydrocarbons therein exist in a single phase and thatin others a portion of the heavy constituents is in a separate liquid phase Whichsometimes remains in the reservoir. The usual method of recovering distillate from a well iiuid produced from such a reservoir is to reduce its pressure, for example by expansion through a valve, with or without auxiliary cooling-and then separate the precipitated liquid from the residual gas. It

is now well understood that this precipitation or condensation upon reduction of pressure is due to the phenomenon known kas retrograde condensation and that there is for every fluid composition and separator temperature a certain pressure at which the condensed liquid hydrocarbons contain a maximum yield of the desired relatively heavy distillate.

ln carrying out operations of this type for the retrograde condensation conditions from the residual gas, but this expedient'is unduly expensive since it entails vthe absorption of all of the moisture from the well iiuid, and consequently the reconcentration of a large volume of antifreeze liquid. Y

f I have found that a large proportion of the v water in a. distillate-containing well-nula can be removed simply and economically by cooling the iiuid to a temperature slightly above the maximum temperature of hydrate formation," and separating the condensed Water therefrom prior to treatment of the fluid for the recovery of lthe further.,

-recovery of distillate hydrocarbons,v it has been found in most instances that satisfactory perorinance of the recovery plant has been seriousiy impeded by the formation and deposition of natural gas hydratesin various portions thereof due to the natural presence of moisture in the Well huid being processed. .Although natural gas hydrates are not completely understoods it may be said that they are solids having the general appearance of snow which form from water and natural gas constituents such as methane and ethane under superatmospheric pressures and at temperatures above the normal freezing point of A water and below a temperature which 'is fairly liquid distillate hydrocarbons. By the selection of suitable conditions of water separation I am able to dispense entirely with the use of anti- I'reeze or dehydrating agents in most cases. although under some conditions they may be desirable to reduce the water content still In the latter instances, however, reconcentration ,costs are kept extremely low.

lt is an object of my invention to provide a novel and economical method of recovering valuable light liquid hydrocarbons -from moisturecontaining well fluids. Another object is to provide improved methods of removing water from high pressure distillate-containing well uids. rifuiftherv object is to provide novel apparatus which is particularly suitable for carrying out my improved methods of distillate recovery. Further I objects land advantages of my invention will be c omprises substantially cooling a moisture-containing well duid produced at a high -well head pressure by a well of the distillate type to a temperature above the maximum temperature of hy- .drate formation of the uid and separating water' in the liquid state from the fluid and Withdrawing it from the system prior to treatment of the latter'for the recovery of valuable light liquid hydrocarbons; Generally speaking, well head pressures of distillate-type wells are in excess of 1500 pounds per square inch and it is preferred to carry out the cooling and water separation steps at pressures of the same order as the well head -pressure, some pressure drop, of course, such as that resulting from the friction of the uid in passing through yheat exchanges, piping, `etc. being unavoidable.

separated will depend upon several factors, one of The amount of water provide a factor of safety I-prefer to cool the well iluid to a temperature not less than 5 F. above and not more than 15 F. above, the maximum temperature of hydrate formation. In this way most of the moisture in the well uid as it is produced can be reduced to the liquid state and separated, and the residual moisture is in most cases insuicient to cause hydrate formation even upon further cooling.

The following example will serve to illustrate the degree of moisture removal obtainable accordng to my invention: The production from a distillate-type well in a Texas eld contained approximately 0.95 barrel of water per million cubic feet of gas. 'I'he temperature at the bottom of the well was about 208 F.- and the cor- 'I'he lower portion of' this range gives the best results, but in order to.

of water therefrom with a liquid dehydrating agent such as calcium chloride or other brine, glycerine. glycol,v etc., andv then separate the dehydrating agent .containing absorbed water from the uid prior to further processing for the recovery of distillate.

Further features and details of my invention v can best be understood from the following description of a preferred embodiment thereof. Referring now to. the drawing, a producingwell I0 is shown which is 'of the distillate type as hereinabove described. The well uid owing therefrom at the well head will be at a relatively high pressure and temperature, for example, about 1500 to 4000 or more pounds per square inch and about 75 F. to 225 F., depending primarily upon the bottom hole temperature and \pres,sure, the welliiuid composition and the rate of production. This duid passes through valve II, 'whichis normally wide open and therefore does not cause any substantial pressure reduction, and line I2 toV cooler I3, in which it is substantially cooled to a temperature above the maximum temperature of hydrate formationof the fluid. The requisite cooling can be suitably obtained by indirect heat exchange with cold responding pressure was about 3100 pounds per square inch, while the Well head temperature and pressure were about 134 F. and about 2700 f pounds per square inch, respectively, when the production rate was 5,000,000 cubic feet per day. 'I'he maximum temperature -of hydrate formation for this fluid was found to be about 83 F. at 2700 pounds per square inch. Cooling this well fluid to about 90 F. and separating the condensed water at about 2700 pounds per square l inch results in the removal of approximately 90% of the moisture content. l

'I'he preliminary cooling step also vcauses the condensation of some liquid hydrocarbons, which separate out in the water seperator together with those present in the uid in the liquid phase at the well head. These liquid hydrocarbons can be removed from the system together with the water or they can be handled separately in a manner which will be described in detail below.

Under some conditions, for example when extremely low temperatures are to'be employed l in the distillate separation operation, it may be desirable to dehydrate the fluid from which most of the water has been removed according to my invention. yThis can be done in any suitable manner including the use of adsorbents or liquid dehydrating agents. Alternatively nor-A mally gaseous antifreeze materials such as ammonia can be used. In any of these cases I am able to reduce the cost of such procedures by my preliminary coolingA and water separation steps. One particularly advantageous method of carrying out an auxiliary dehydration is to contact the high pressure fluid after separation water or other cool streams which may be available, and preferably the cooling is suflicient to lower the ltemperature of the well iiuid to a point above, but not more than about 25 F.v above Ithe maximum temperaturev of hydrate formation, the range from about 5 F. to 15 F. above the maximum temperature of hydrate formation being most d-esirable. The .cooled uid ows through line I4 into water separator I5.

The fluid entering separator I5 contains liquid material including not .only water, but hydrocarbons as well, andthe source of these liquids will be. discussed briefly. It is well-known that the uid pressure at the well head decreases as the rate of production increases, the pressure drop between well bottom and head ranging u p to 1000 pounds per square inch or more at high rates of production and the temperature drop often being 'in the neighborhood of 50 F. to

F. In most cases such pressure and temperature drops will cause the condensation of some water and hydrocarbons as the well uid i'lows upward through the tubing. Often hydrocarbon and/or aqueous material enters the base of the well in the liquid phase and this material is also contained in the well uid as produced.

Finally the temperature reduction in cooler I3 from the Well fluid therein will settle to the bottom and stratify to form a lower aqueous layer and an upper hydrocarbon layer. 'I'he lower layer is withdrawn from the system through valve I6, which is controlled by liquid level control I1, and line I8, control II being equipped with a float having a density between that of Water and that of the hydrocarbons in the upper layer. 'I'he hydrocarbon layer is withdrawn from separator I5 by means of valve I 9 controlled by liquid level control 20 and line 2|, and this material can also be removedv from the system as a valuable product through valve 22 and line 23. However, the hydrocarbon fraction in line 2| is very wild, i. e., it contains excessive amounts tion.'

of normally gaseous hydrocarbons such as methane and ethane, so that it is preferred to close valve 22 and pass it through line 24 for a further treatment within the system which will be described below.

The well fluid remaining in the vapor phase, which contains most of the desired liquid hydrocarbons but is now relatively free from water, is withdrawn from the upper portion of separator I through line 25 and ows through valve 26 and line 21 to the. distillate-recovery opera- In the form of my invention now being described valves 28 and 29 vin branching lines 30 and 3l are closed and valve 26 is fully open so that the fluid in line 21 is-still at a high pressure of the order of the well head pressure,

As stated above the desired distillate can be condensed 4by expanding the well uid after the removal of water according to my invention. The expansion necessarily cools the fluid also due to the Joule-Thomson effect, and in Asome cases no auxiliary cooling will be required to obtain the desired temperature and pressure for the separation of distillate, but in others further cooling will be necessary and this is preferably done prior to expansion. The expansion step can be carried out using an expansion valve or orice, or an expansion engine can be employed so that the well iluiddoes useful mechanical work, and the latter procedure is very advantageous since this type of expansion results in greatly increased cooling. For purposes of simplicity, however, ordinary cooling and expansion apparatus will be described, the fluid in line 21 being iirst cooled in cooler 32 and passed through line 33, expansion valve 34 and line 35 to distillate separator 36. Due to the removal of most of the water from the'well fluid according to my invention, the formation of natural gas hydrates during these steps is substantially eliminated. The cool expanded fluid enters separator 36 at the pressure and temperature at which it is desired to separate distillate therefrom. Under most circumstances these will be in the range from about 500 to about 1500 pounds per square inch and from about 100 F. to about +50 F., but other conditions can be used.

Separator 36'is of type such that equilibrium between liquid and vapor phases is substantially reached, the pressure therein being controlled by valve 31 in residual gas line 38. The liquid hydrocarbon condensate settles to the bottom of separator 36 and is Withdrawn by means of valve 39 controlled by liquid level control 40 and line 4i to the stabilization portion of the system. The hydrocarbon fraction in line 24 can be introduced into line 85 by means of line 42 and valve 43, or it can be passed directly into line @il through valve fili. The former procedure is more advantageous since a slightly greater ultimate yield of stabilized distillate is obtained thereby.

The distillate fraction in line di can be passed through line d5, valve d6, line Il?, heat exchanger de, line :t8 and heater 50 *to stabilizer 5l or some of the gases having an excessively high vapor pressure can be removed by flashing at a lower pressure prior to introduction into stabilizer 5i. The latter procedure is usually preferable and can be accomplished by closing valve d6 and opening valves 52 and 53 whereupon the distillate in line il passes through line ed and valve 52 into separator 55 which. is maintained under a pressure controlled by back pressure control l valve e8 in line 51 at some value less than that is Withdrawn from separator 55 through valve 58 which is controlled by liquid level control 59 and' through valve 53 to line 41, whence it passes through heat exchanger 48 wherein its temperature is raised by indirect heat exchange with hot stabilized distillate from stabilizer; 5l. Supplemental heat is added if necessary by means of heater 60.

Stabilizer 5| can be of conventional design and ls preferably operated at about 200 to 400 pounds per square inch, for instance 350 pounds per square inch. Heat is applied to the bottom of the stabilizer by means of heating coil 60 and reflux is provided for example by means of dephlegmating coil 6I. The stabilized distillate passes from the tower bottom through line 62,

valve 63, heat exchanger 48, cooler 64 and line 65 ;to distillate storage 'tank 66. While' I have shown stabilizer 5l as my preferred means of producing distillate of a quality meeting specifications, the same product can be obtained although with lower yields by iurther stages of expansion and separation in a manner well known in the art., and this procedure is also contemplated as an alternative method.

The residual gas from distillate separator 36 in line 38 is preferably compressed by means of compressor 61 to a pressure which allows its reinjection into the same or another producing formation through line 68, valve 69 and input well 10. Recycling in this manner greatly increases the total yield of liquid hydrocarbons recoverable from a producing formation and its advantages are now universally recognized. Generally speaking, it will be desirable to recompress and reinject the gas from separator 55 and this can be done by means of compressor 1I which raises the pressure of gas from line 51 and delivers it to line 68 through line 12 and valve 13. The overhead from stabilizer 5I is withdrawn through pressure control valve 14 and line 15Vand can be Withdrawn for fuel or any other suitable purpose through line 16 and valve 11. Alternatively the gas in line 15 can be reinjected Iby closing valve 'I1 and opening valve 18 in line 19 or the gas in line 51 can be withdrawn from the system throughv lines 19 and 16 by closing valve 13 While keeping valves 11 and 18 open.

It is apparent from the above that I have described va simple and eicient system for recovering distillate from moisture-containing well uids according to my invention which substantially eliminates the problem of hydrate formation under most conditions. As explained above, however, it may be desirable under certain circumstances to carry out a separate dehydration operation on the well fluid after the removal of most of the Water therefrom, and the drawing includes apparatus for accomplishing this in a preferred manner.

In this modification valve 26 is closed and valves 28 and 29 opened, so that the iluid in line 25 removed from the upper portion of water chloride brine, glycerine, glycol, etc.,1f/or mixtures thereof, is supplied to the upper portion of tower by means of line 8i and flows down the tower countercurrent to the ascending fluid, thus removing a substantial part of the remaining moisture therefrom. By suitable regulation of the dehydrating agent concentration, ratio of dehydrating agent to well uid, etc., any desired amount of moisture removal can be achieved. Dehydrating agent collects in the bottom `of tower 80 and is withdrawn through valve 82, which is controlled byy liquid level control 8.8, and line 84, from which all or a portion of it can be returned to line 8| by means of valve 85, line 88, pump 81, line 88 and cooler 89. Cooler 88 may not be necessary in some cases but is advantageous when the dehydrating agent would otherwise be at` a temperature above that of the well uid in tower 88, for instance when reconcentrated dehydrating agent is used. All or a part of the dehydrating agent in line 84 can also be directed by means oi' line 90, valve 8| and line 82 into reconcentrator ll, which can be of conventional design and is therefore not shown in detail. The reconcentrated dehydrating agent passes through line 94 and valve 95 to pump 81 for recirculation. Fresh dehydrating agent to ll the system and for make-up is supplied through line 96 and valve 81. Y l

Many details which have been omitted in the aboveA description have not been given in order tol simplify the description, but such details, for instance the construction and operation of the apparatus according to my invention lfor any particular well uid or fluids, theiuse of available plant streams for cooling or-heating by indirect heat exchange, etc., can be easily supplied by those skilled in the art. I contemplate also as a part of my invention all modifications within the spirit thereof, such as the use of high pressure absorption or other` methods for the recovery 'of distillate from the relatively dry well iluid, the substitution of two'separators for the water separator I5, or of a mixer-separator system for contact tower 80. By high pressure absorption I mean the contacting of the well uid at a relatively high pressure, for example 1000 pounds per square inch or more and preferably in excess of 1500 pounds per square inch, with a liquid absorption mediuml less volatile than the distillate to be recovered, and separation of the enriched absorption medium from the residual gas. In many cases the absorption step can be carried out without first reducing the pressure on the relatively dry well uid, but further cooling is almost always advantageous.

It is obvious that the uid from a plurality of distillate wells can be combined and the distillate recovered therefrom accordingto my invention in the same mannerr as hereinabove described for the fluid from a single well, and that a plurality of input wells can likewise be used.

While I have described my invention in connection with certain embodiments thereof, it is to be understood that these are by way oi.' illustration and not by way of limitation, and that I do not means to be bound thereby but only by the j appended claims in which I have deiined my invention.

I claim:

1. Apparatus for recovering liquid hydrocarbons from a moisture-containing uid produced by a well of the distillate type at a high well head pressure comprising means for cooling said l fluid at high pressure, a high pressure separator,

means for introducing said cooled fluid into said separator, means for removing condensed water tion and a residual gas from said second separator.

2. The-method oi recoveringliquid hydrocarbons from'a uid producedvby a well of the distillate type at a high well headfpressure and containing substantial amounts of water which comprises substantially cooling said iluid to a temperature above the maximum temperature of hydrate formation of said iiuidfwhereby a major portion of the water in said uid is condensed, introducing said cooled uid into a separating zone, removing a stream consisting essentially of liquid water from said separating zone and from the system, separately removing agas stream consisting essentially of hydrocarbons from qsaid separating zone, contacting said separated gas Y stream at a pressure in excess of 1000 pounds per square inch with a liquid absorption medium less volatile than the liquid hydrocarbons to be recovered, and separating the enriched absorption medium from the residual gas.

3. The method of claim 2 wherein said fluid is cooled toa temperature not more than 25 F. above the maximum temperature of hydrate formation of said uid.

, 4. The method of e recovering liquid hydrocarbons from a iluid produced by a well of the distillate type at a high' well head pressure and containing substantial amounts of water which comprises substantially cooling said uid to a temperature above the maximum temperature of hydrate formation of said fluid, whereby a major portion of the water in said fluid is condensed, introducing said cooled uid into a separating zone, removing a stream consisting essentially of liquid water from said separating zone and from the system, separately removing a gas stream consisting essentially of hydrocarbons from said separating zone, contacting said separated gas stream with a. liquid dehydrating agent to remove further quantities of water therefrom, separating said dehydrating agent from the further dehydrated gas stream, and recovering liquid hydrocarbons from said further dehyinch with a liquid absorption medium less volatile than the liquid hydrocarbons to be recovered,l and separating the enriched absorption medium from the residual gas.

7. 'I'he method of claim 4 wherein the step of recovering liquid hydrocarbons includes expanding said further dehydrated gas stream whereby liquid hydrocarbons are condensed therefrom by virtue of the retrograde condensation eiiect. and separating said liquid hydrocarbons from the residual gas.

RILEY FLOYD FARRIS. 

